The invention generally relates to safety ground support systems for highway signs, utility poles and the like, and more specifically to a load profile break safe breakaway system.
U.S. Pat. No. 3,951,556, owned by the Assignee of the subject application, discloses a load concentrated breakaway coupling apparatus. The aforementioned patent contains a discussion of the background of such highway post supporting devices and the problems which need be overcome. While the breakaway coupling assemblies disclosed in the patent under discussion have proved extremely satisfactory and have met safety standards established by various governmental transportation agencies, there has recently been a trend for consumers to purchase and drive smaller automobiles. The so-called compact and sub-compact automobiles are generally positioned lower or closer to the ground as compared with the larger and medium sized cars causing higher incidences of snagging.
In the above mentioned U.S. Pat. No. 3,951,556, the mathematical relationships are discussed which make it possible for the breakaway system to balance the clockwise and counter-clockwise torques at the breakaway assemblies caused by wind loads, while producing bending moments which sever the breakaway couplings upon impact forces applied proximate to the breakaway couplings. It has been found that it is desirable to lower the breakaway couplings as low as possible to the footings on which the posts are mounted to accommodate the smaller compact and sub-compact automobiles.
In accordance with one system which has been proposed to lower the heights of the breakaway couplings, there are provided a plurality of bolts the major portions of which are embedded in the footing concrete, the upwardly projecting exposed ends being externally threaded. The couplings are provided, at their lower portions thereof, with internally threaded openings which are adapted to threadedly mesh onto the upwardly extending footing bolts. This proposed system has a number of disadvantages. For example, when sufficiently high bending moments are applied to the exposed footing bolt portions, these bend and are rendered essentially unusable. To replace the footing bolts, it is practically necessary to destroy the footing in order to extract the embedded portions of the bolt.
A post mounting system, similar to the system just described, is sometimes referred to as the "New Jersey System". This system is similar to that just described with the exception that the lower portions of the breakaway couplings, those threadedly meshed with the anchor bolt projecting portions, are embedded within a layer of grout. Clearly, while the use of the grout is an attempt to raise the level of the footing to the finished ground line, the addition of the grout in a way which covers the portions of the couplings below the necked down portion or the zone of weakness complicates replacement of the post on new couplings following impact.